Mixed-initiative assistants can be applied to a variety of information-rich problem-solving tasks on the Web, such as travel planning and equipment purchasing tasks. A mixed-initiative environment for such tasks can greatly improve the decision making environment for a user if the application is designed to meet the needs of a user. However, each user has different needs and preferences, making it difficult to design a single application for all users. Thus, we are applying the mixed-initiative paradigm recursively to develop a mixed-initiative system for building mixed-initiative systems. This paper describes the basic framework for constructing mixed-initiative systems, which is based on our previous work on developing mixed-initiative information assistants in Heracles. The new system, called Alcmene, will be implemented as an application of Heracles and will allow a user to author a new Heracles application through a mixed-initiative problem-solving process.